This invention has its basis in a discussion of developing a solid state device that utilizes a non-filtered light source of monitor in a transcutaneous manner the physiological status of gas in the blood of a human being. The purpose is to develop a more reliable method and apparatus to determine the onset of apnea and cyanosis in a non-invasive manner.
The definitions of apnea, cyanosis and transcutaneous as stated in Webster's 7th New Collegiate Dictionary, copyright 1965 by G & C Merriam Company are as follows:
Apnea or Apnoea, (n)--transient cessation of respiration; (adj.)--Apneic PA1 Cyanosis, (n)--dark blue color, a bluish or purplish discoloration (as of skin) due to deficient oxygenation of the blood; (adj.)--Cyanotic PA1 Transcutaneous, (adj.)--entering through the skin (infection) (innoculation).
We investigated commercially available apnea monitors. Our investigation showed that there was no apnea monitor which used non-filtered light from two sources of different wave lengths to indicate the onset of apnea and cyanosis. A number of articles have been written on "Sudden Infant Syndrome" which has been given the acronym SIDS or "Crib Death". It is estimated that 10,000 babies in the United States die every year from SIDS.
A number of articles have been written on SIDS and also apnea monitors. In the August-September 1980 issue, Volume 5, No. 10 and 11, of HEALTH DEVICES, published monthly by the Emergency Care Research Institute, 5200 Butler Pike, Plymouth Meeting, PA 19462 and in the "WESTERN HEAlTH NEWS", September 1081, published monthly by Syndicate Magazines, Inc. 6 E. 43rd Street, New York, NY 10017, are two interesting articles. Again, there have been numerous articles published on SIDS.
In the "HEALTH DEVICES" article it was stated: "Most apnea monitors in the market today operate via impedance pnumography. A small current in the 20-120 kHz frequency range is passed across the thoracic cavity. The small impedance changes due to air entering and leaving the lungs, and "blood welling" from pressure changes in the thoracic cavity are carried by this current as a voltage change. This change is, in turn, interpreted by the monitor as a breath."
If the baby does not breathe for a period of time lasting longer than about twenty seconds there may occur, if the episodes are left unchecked, a life threatening progression of hypoxia, brain damage and death.
If the baby dies the effect upon the parents and the relatives may be severe. For example, the parents and relatives may go into a deep depression or have a complete mental breakdown or a lifelong guilt feeling haunted by the thought that the baby's death may be somehow their fault. Another side effect is that the death of the baby may lead to divorce between the parents and the breakup of the family.
After the investigation we found that we could use light emitting diodes as a source of the desired wave length as contrasted with impedance pneumography.
We investigated the color change in blood, viz., hemoglobin, with the increase in carbon dioxide in the blood. The color of the hemoglobin changes from a red where there is oxyhemoglobin to a blue where there is carboxyhemoglobin. With the change in the color of the blood from red to blue there is an indication of an increase in the concentration of carbon dioxide in the blood. With an infant, a child less than one year old, there is little calcium in the bones and the light will pass through the tissue and also the solid matter of the bone to be. This is so with respect to the toe of an infant less than one year of age. A light will pass through the tissue and also the material which will become bone upon the maturing of the infant. In this manner it is possible to detect and to monitor the change in color of the blood and use this as an indication of the buildup or increase in concentration of carbon dioxide in the bloodstream.
Apnea is the episodic or cylical episode in the cessation of breathing. In an infant this is more critical than in an adult as an infant breathes more rapidly than an adult, or it may be stated, that the frequency of breathing with an infant is greater than the frequency of breathing with an adult. A result of this is that with an infant it is more critical to have an adequate exchange of oxygen or carbon dioxide in the bloodstream. With an adult the frequency of breathing is in the range of eight to twelve times per minute. With an infant less than one year of age the frequency of breathing is in the range of twenty to thirty times per minute. As a result an infant less than one year of age who has apnea for just a few seconds misses the vital transfer of oxygen for carbon dioxide in the bloodstream.
In the normal brain the medulla is a control center for sending of electrical impulses to the respiratory system for expansion and contraction of the lungs to take in fresh air with a high concentration of oxygen and to exhale gas with a higher concentration or carbon dioxide than the fresh air. The medulla receives its signal based on the amount of carbon dioxide in the blood. In a baby that has missed breathing for five or six seconds there is a buildup in the concentration of carbon dioxide in the bloodstream. Another way of stating this is that the baby may have missed two cycles of breathing. As a result there is an increase in the concentration of carbon dioxide in the bloodstream and a threat to the life of the baby. If this increase in the concentration of carbon dioxide in the bloodstream occurs in a chronic situation then the medulla becomes conditioned so as to ignore some of the signals to it to the effect that there is an unusually large increase in the concentration of carbon dioxide in the bloodstream. With the medulla so conditioned then the medulla may not, promptly, send signals to respiratory system to inhale fresh air having a low concentration of carbon dioxide. In other words, the increase in the concentration of carbon dioxide in the blood acts as a carbon dioxide drive mechanism in the brain. The result is that the medulla does not send the appropriate signals to the respiratory system. A terminal result of this increase in the carbon dioxide in the blood is the death of an infant. It is possible to try to resuscitate the infant but because of the high concentration of carbon dioxde in the blood the brain does not respond to the resuscitation efforts and the infant or victim cannot be revived.
With this belief and knowledge we consider that it is necessary to have a detection system for detecting the increase in the concentration of carbon dioxide in the blood and also an accompanying warning system. The detection system and the warning system must detect the increase in the carbon dioxide in the blood within the time period of five or six seconds and emit a warning. If the increase in carbon dioxide in the blood is not detected in about five or six seconds the result may be a fatality.
With this information and belief we consider that if it be possible to detect the increase in the concentration of carbon dioxide in the blood then a stimulus may be applied to the infant and the infant will inhale and take fresh air into the lungs. The stimulus can be of a non-invasive auditory nature and not an electrical nature.
Prior to this invention, and to the best of our information and knowledge, the apnea monitors and sensing units relied upon impedance pneumography. Further, there was a time delay of approximately ten to thirty seconds so that in that time period there was a large increase in the concentration of carbon dioxide in the blood of the infant. This large increase in the concentration of carbon dioxide in the blood of the infant made it difficult, if not impossible, to resuscitate the infant.
The commercially available apnea monitors give a quantitative indication of the frequency of respiration of the infant. Our apnea monitor gives a qualitative indication of the change of the concentration of carbon dioxide in the blood. Our apnea monitor will function within the first five to six seconds of the increase in the concentration of the carbon dioxide in the blood.
Our above comments with respect to the infant are also applicable to an adult suffering from apnea. The frequency of breathing of an adult is less than the frequency of the breathing of an infant but at certain times with an adult there may be apnea and our invention can be used to overcome the apnea of an adult. An example of this is an individual who snores heavily. If the individual stops snoring heavily he may be having an apnea episode. One way of relieving this individual of the apnea episode is to shake the individual or agitate the individual or stick an elbow in the ribs of the individual to start the individual breathing again. This condition is referred to as "sleep apnea".